The present invention relates to an image forming apparatus utilizing electrophotographic method.
In the image forming apparatus utilizing electrophotographic method, an image on an image carrier, such as a photosensitive member or an intermediate transfer member is transferred onto a transfer material, such as a paper sheet to form the image onto the transfer material. When increasing an image forming speed or minimizing the size of the apparatus, there is a problem that in the transfer position where the image is transferred, the image quality deteriorates due to the disturbance of the image caused by the vibration of the rear edge of the transfer material.
In the Japanese Patent Publications Open to Public Inspection Nos. 61-188345 and 8-76607, this problem was pointed out and the countermeasures to the problem have been proposed.
Namely, in the Japanese Patent Publication Open to Public Inspection no. 61-188345, it is proposed to provide a guide plate (a sheet having elasticity, such as PET) for softly pressing the transfer material to the transfer position in the guiding section.
In the Japanese Patent Publication Open to Public Inspection No. 8-76607, it has been proposed to fix a guiding member formed by an elastic body to the edges of a pair of guiding plates for guiding the transfer material to the transfer position and to bend the free edge of the guiding member with a predetermined angle.
The image quality deterioration caused by the vibration of the rear edge of the transfer material will be described by using FIG. 3, which illustrates the transfer section of an image forming apparatus of the embodiment of the invention and FIG. 1, which illustrates an example of image quality deterioration.
In FIG. 3, a registration roller 23 transfers a transfer material P to the transfer position TR formed by a transfer roller 7A and a support roller (an earth roller 61), and a toner image is transferred onto the transfer material P from an intermediate transfer member 6.
Numerals 30 and 31 are a pair of guiding plates for guiding the transfer material P between the registration roller 23 and the transfer position TR, the pair of guiding plates being formed by a metal plate, which is a rigid body.
When the rear edge of the transfer material P leaves from the registration roller 23, the rear edge of the transfer material leaps up and vibrates, which causes toner scattering and transfer shifts. The toner scattering is a phenomenon that dots are formed in the non-image area as shown in FIG. 1(a). The transfer-shift is the phenomenon that the image shifts as shown in FIG. 1(b). It is known that the phenomenon occurs when the rigidity of the transfer material P is high in case the transfer material P is a thick paper sheet. The suppression effect of the toner scattering and the transfer shift will be obtained by suppressing the leap-up of the rear edge of the transfer material P by providing the guiding member 32 formed by the elastic body at the front edge of the upper support member 31, namely by providing the guiding member 32 at the down stream edge of the transfer material conveyance direction, the leap up of the rear edge of the transfer material is suppressed and the suppression effect of the toner scattering and toner shift is obtained.
In recent years, as a results of that the performance of the image forming apparatus has been improved, namely as a results of the diversity of utility categories for using color documents and for forming document other than the document for office use, only the countermeasures disclosed in the Japanese Patent Applications Open to Public Inspection S61-188345 and H8-76607 are not enough. Particularly, as a result of the diversity of the kinds of the transfer materials, which are used in the image forming apparatus, when the toner image is transferred onto a thick transfer material, the transfer shits and the toner scattering caused by the leap-up of the rear edge of the transfer material become problems.